In many storage systems, data is distributed across multiple storage devices in accordance with redundant array of independent disks (RAID) arrangements. Some RAID arrangements allow a certain amount of lost data to be rebuilt from parity information, typically in response to a storage device failure or other type of failure within the storage system. It is desirable in certain contexts to be able to “prefill” at least a portion of a RAID array with random data. For example, such prefilling is desirable prior to performing various performance tests at regular intervals, including while varying the hardware or software used on that RAID array. Due to the nature of a RAID array, its performance can be drastically different based on how full the array is and whether or not the individual blocks have been used previously. Unfortunately, conventional techniques for prefilling the RAID array with suitable amounts and types of data are inefficient and unduly time consuming.